Objective: The objective of these experiments is to understand the synthesis, assembly, and secretion of IgA by mouse myeloma cells. Using cultured cell lines, clones will be isolated which differ quantitatively or qualitatively in their production of immunoglobulin from the parent line. By using IgA lines which bind specific antigens, variation in the antigen binding capacity of myeloma immunoglobulins can be specifically studied. Approach: The cells from mouse myeloma tumors are adapted to grow in continuous culture. These cultured cells can be cloned at high efficiency in soft agar on rat embryo fibroblasts. By overlaying the developing clones with specific antiserum or antigen, clones can be identified microscopically which are secreting an immunoglobulin which reacts in an altered fashion with specific antiserum or antigen. These clones can be recovered, grown to mass culture and their immunoglobulins characterized using: 1) SDS gels, 2) isoelectric focusing, 3) quantitative antigen binding, and 4) antisera of differing specificities.